Field of the Invention
The invention relates to a radiation-sensitive mixture and the use of this radiation-sensitive mixture.
In the structuring of semiconductor components on an industrial scale, photosensitive mixtures comprising a base polymer and a photoactive (radiation-sensitive) component, so-called photoresists, are used. First, a layer of the photoresist is produced on the substrate to be structured and the image of a mask is projected into this layer by means of a suitable exposure unit. A latent image is formed by photochemical modification of the photoactive component in the layer. Depending on the tonality of the photoresist system (positive or negative), the exposed or the unexposed parts of the latent image are then dissolved away (developed) by means of a suitable developer, if necessary after a heating step. The relief structures thus obtained in the photoresist layer show the positive or negative image of the mask and in turn serve as an etch-resistant mask for structuring the substrate by means of suitable etching medium. An important precondition for photoresists having good structuring properties is, inter alia, high transparency of the base polymer at the exposure wavelength, as described in European Patent Application EP 0 388 484 A1, for example for polymers containing anhydride groups in a positive photoresist.
Proc. SPIE Vol. 2724 (1996), pages 296 to 307, describes a base polymer having 1,2-dicarboxylic acid monoester units for use in negative photoresists processible in an aqueous medium. A layer consisting of the polymer and a photosensitive acid, i.e. a compound which liberates a strong acid on exposure to light, is subjected to a heating step after structuring exposure, anhydride groups being formed under acid catalysis in the exposed parts. During the aqueous development, the unexposed parts are then selectively dissolved. The production of positive structures is however not possible with polymers of said type since the ester radicals used cannot be converted into free 1,2-dicarboxylic acid units under acid catalysis.
Owing to the unevenness and high reflectivity of semiconductor substrates, the two-layer technique is used in fine structuring. First, a planarizing and absorbing polymer layer which serves as a substrate for a thin photoresist layer (top resist) is produced on the substrate. This photoresist layer can be exposed under ideal exposure conditions (planar and light-absorbing substrate, thin layer within the depth of focus ensures crisp image). After the development, positive or negative structures with high resolution are obtained in the top resist. These structures are silylated in a separate wet-chemical step, as described in European Patent Application EP 0 395 917 A2, i.e. silicon is chemically bonded to the base polymer by means of a silicon-containing reagent; at the same time, the structures experience an adjustable lateral expansion. This ensures that the top resist structures can be transferred in an anisotropic oxygen plasma to the planarizing polymer layer, and structures having a high aspect ratio and very high resolution are obtained. An important precondition for the silylatable top resist is the use of a base polymer having reactive groups, as described in European Patent Application EP 0 388 484 A1, for example for polymers containing anhydride groups.
The so-called TSI technique (top surface imaging) has the same benefits as the two-layer technique but additionally has the advantage of a simplified process. First, a photosensitive photoresist layer is applied to the semiconductor substrate. During the structuring exposure, a latent image is then produced only in the top surface. This image is silylated, directly after exposure, in the exposed (negative) or unexposed (positive) parts, depending on tonality, as described, for example, in European Patent Application EP 0 394 740 A2 and European Patent Application EP 0 492 256 A1.
The actual development is carried out in an anisotropic oxygen plasma, structures having a high aspect ratio and very high resolution being obtained. An important precondition for a silylatable photoresist is the use of a base polymer having reactive groups, as described in European Patent Application EP 0 388 484 A1, for example for polymers containing anhydride groups.
In the case of the so-called chemically amplified photoresists (cf. for example U.S. Pat. No. 4,491,628), a small amount of an acid is produced photochemically in the photoresist layer from an ionic or nonionic photoactive acid generator by means of a small exposure dose. In a post-exposure bake (PEB), this acid effects the catalytic elimination of a protective group on the polymer and hence the change from hydrophobic to hydrophilic which is necessary for the development. By development in an alkaline developer, the exposed hydrophilic parts are dissolved and a positive image of the mask is obtained, whereas, with the use of an organic solvent as developer, the unexposed hydrophobic parts are dissolved and a negative image is obtained. In particular, tert-butoxycarbonylmaleimido groups (European Patent Application EP 0 492 253 A1), tert-butyl ester groups (European Patent Application EP 0 494 383 A1) and tert-butoxycarbonyloxystyrene groups (U.S. Pat. No. 4,491,628) are used as acid-labile protective groups.
In the case of the photoresist materials known to date, i.e. radiation-sensitive mixtures, either the exposed or the unexposed parts are thus dissolved with aqueous alkaline developers. The corresponding negative image can be produced by using organic solvents. However, this option is not feasible since an expensive safety procedure is associated therewith in wafer production. Thus, two different developers (aqueous or organic) have been required to date for the dual tonality of a resist material.